Highly Stable, Water-Soluble CdSe/ZnS/CdS/ZnS Quantum Dots with Additional SiO2 shell

Quantum dots (QDs) are fluorescent nanocrystals extensively used today in research and applications. They attract much interest due to the high photostability and fluorescence quantum yields close to 100%. The best QDs are made by synthesis in organic media, and they have to be transferred into aqueous solutions if biomedical applications are concerned. An advanced method for rendering QDs water-soluble is to coat them with hydrophilic SiO2 -layer. However, growing a silica shell with a predetermined thickness is a problem, because uncertain values of the molar extinction coefficients (ε) of core/shell QDs made it impossible to calculate precise yields of the chemical reactions involved. Here we suggest an approach to solving this problem by constructing the structural models of per se and silica-coated QDs followed by measuring ε in a course of the QD synthesis, thus carrying out precise quantitative reactions. Proceeding in such a way, we prepared the CdSe/ZnS/CdS/ZnS QDs with the structure predicted by the model and coated by silica shell. Prepared QDs are characterized by a narrow size distribution and the same fluorescence parameters as the original QDs in the organic medium. Developed approach permitted efficient QDs water-solubilisation and preparation of stable nanoparticles for plethora of biomedical applications.     Keywords: Quantum dots, QD, silica shell, core-shel

Nonsteady condensation and evaporation waves

We study motion of a phase transition front at a constant temperature between stable and metastable states in fluids with the universal Van der Waals equation of state (which is valid sufficiently close to the fluid's critical point). We focus on a case of relatively large metastability and low viscosity, when it can be shown analytically that no steadily moving phase-transition front exists. Numerically simulating a system of the one-dimensional Navier-Stokes and continuity equations, we find that, in this case, the nonsteady phase-transition front emits acoustic shocks in forward and backward directions. Through this mechanism, the front drops its velocity and eventually comes to a halt. The acoustic shock wave may shuttle, bouncing elastically from the system's edge and strongly inelastically from the phase transition front. Nonsteady rarefaction shock waves appear in the shuttle process, despite the fact that the model does not admit steady rarefaction waves propagating between stationary states. If the viscosity is below a certain threshold, an instability sets in, driving the system into a turbulent state. This work was supported by the Japan Society for Promotion of Science.Comment: revtex text file and four eps files with figures. Physical Review Letters, in pres

Coherent Radio Pulses From GEANT Generated Electromagnetic Showers In Ice

Radio Cherenkov radiation is arguably the most efficient mechanism for detecting showers from ultra-high energy particles of 1 PeV and above. Showers occuring in Antarctic ice should be detectable at distances up to 1 km. We report on electromagnetic shower development in ice using a GEANT Monte Carlo simulation. We have studied energy deposition by shower particles and determined shower parameters for several different media, finding agreement with published results where available. We also report on radio pulse emission from the charged particles in the shower, focusing on coherent emission at the Cherenkov angle. Previous work has focused on frequencies in the 100 MHz to 1 GHz range. Surprisingly, we find that the coherence regime extends up to tens of Ghz. This may have substantial impact on future radio-based neutrino detection experiments as well as any test beam experiment which seeks to measure coherent Cherenkov radiation from an electromagnetic shower. Our study is particularly important for the RICE experiment at the South Pole.Comment: 44 pages, 29 figures. Minor changes made, reference added, accepted for publication in Phys. Rev.

An alginate-layer technique for culture of Brassica oleracea L. protoplasts

Ten accessions belonging to the Brassica oleracea subspecies alba and rubra, and to B. oleracea var. sabauda were used in this study. Protoplasts were isolated from leaves and hypocotyls of in vitro grown plants. The influence of selected factors on the yield, viability, and mitotic activity of protoplasts immobilized in calcium alginate layers was investigated. The efficiency of protoplast isolation from hypocotyls was lower (0.7 ± 0.1 × 106 ml−1) than for protoplasts isolated from leaf mesophyll tissue (2 ± 0.1 × 106 ml−1). High (70–90%) viabilities of immobilized protoplasts were recorded, independent of the explant sources. The highest proportion of protoplasts undergoing divisions was noted for cv. Reball F1, both from mesophyll (29.8 ± 2.2%) and hypocotyl (17.5 ± 0.3%) tissues. Developed colonies of callus tissue were subjected to regeneration and as a result plants from six accessions were obtained

Stabilization of Ti5Al11 at room temperature in ternary Ti-Al-Me (Me = Au, Pd, Mn, Pt) systems

Ti$_5$Al$_{11}$ is known as a high-temperature phase in binary Ti-Al alloys. However, its existence at low temperatures was previously observed in ternary Ti-Al-based systems alloyed with some transition metals. In this study, we systematically evaluated Ti-Al-Me ternary systems (Me = Au, Pd, Mn, or Pt) to determine the influence of transition elements on low-temperature stabilization of Ti$_5$Al$_{11}$ phase. The temperature ranges in which Ti$_5$Al$_{11}$ existed in Ti-Al-Me systems were experimentally found using in situ synchrotron X-ray diffraction (SXRD). It was established that addition of Mn and Pt retains Ti$_5$Al$_{11}$ at room temperature. The obtained data were compared with predictions of density functional theory (DFT). The total energy, volume, and bond length are especially significantly reduced by addition of Mn and Pt. Ti5Al11 compound containing both of these elements is less prone to saturation with Ti upon preserving the lattice tetragonality and suppressing Ti$_5$Al$_{11}$ → TiAl transformation. These factors finally contribute to the retention of this phase at room temperature

Joining Ti-based metallic glass and crystalline titanium by magnetic pulse welding

Due to low thermal stability and limited critical size, metallic glasses (MGs) are frequently considered for reinforcing composites. The production technology of composites should provide the minimum heat input to preserve the disordered structure of MGs. In this study, the solid-state magnetic pulse welding (MPW) was used to join crystalline titanium and Ti-based MG. The amorphous structure of the MG layer after MPW was confirmed by synchrotron X-ray radiation diffraction (XRD), ultra-small-angle X-ray scattering (uSAXS), and transmission electron microscopy (TEM). Crystalline particles were found only in the mixing zones subjected to the strongest heating during welding. The average size of the crystalline precipitates was about 25 nm, and their phase composition corresponded to a-Ti. In addition to Ti particles, titanium oxides and nitrides could form at the interface of Ti and MG layers during MPW